1. Field of the Invention
This invention relates to a process of controlling the slag in a top-blowing steelmaking converter comprising at least one blowing lance, which is spaced above the surface of the bath at a distance therefrom which is controlled to ensure a desired progress of the refining process, wherein said distance is adjusted in dependence on the sound level which is due to the blowing noise and is measured through the slag layer at selected frequencies and the oxygen supply rate is optionally adapted.
2. Description of the Prior Art
In a top-blowing steelmaking converter the refining progress depends mainly on slag reactions. For this reason the formation and maintenance of a foamy, reactive slag, the control of the distance of the blowing lance from the surface of the molten bath, which distance has a significant influence on the slag control, and the control of the rate at which oxygen is supplied through the blowing lance are of high significance. At the beginning of the blowing operation a relatively high oxidation of iron and a low oxidation of carbon are desired in order to effect a dissolution of the lime which has been added. An increasing decarburization must be effected as the blowing operation proceeds and a proper decarburization rate must be maintained in order to ensure a desirable slag level and to avoid a slopping. For this reason the distance of the lance from the surface of the molten bath is decreased as the slag level rises after the beginning of the blowing operation. Because the slag which has formed will damp the blowing noise, the sound level which has been measured through the slag can be utilized for a control of the slag, particularly because the sound level of the blowing noise which is damped by the slag, which sound level may be measured at predetermined frequencies, will also depend on the composition of the slag. For this reason the sound level of the blowing noise which is damped by the slag and is measured at defined frequencies can be used for a control of the distance of the lance from the surface of the molten bath in such a manner that a proper reactive fluid slag will be obtained in each stage of the blowing process. But the state of the slag will be influenced by numerous variables and constantly changes. For this reason a control of the lance only in dependence on the sound level of the blowing noise which is damped by the slag is not sufficient for ensuring that slopping will be prevented, as is required.